Method and system for tint control for component video signals

ABSTRACT

A method and system are provided for controlling tint of component video signals. The system includes a first input for receiving a first component video signal; a second input for receiving a second component video signal; circuitry including a first differential amplifier and a second differential amplifier for receiving the first and second component video signals from the first and second inputs, respectively; a first output connected to the circuitry for outputting a first tint control adjustment signal for the first component video signal; and a second output connected to the circuitry for outputting a second tint control adjustment signal for the second component video signal. The first outputted signal is represented as V+kU−2ckU and the second outputted signal is represented as U−kV+2ckV, where V represents the first component video signal, U represents the second component video signal, k is a constant, and c is a value greater than or equal to zero and less than or equal to one.

BACKGROUND OF THE INVENTION

1. Technical Field

The present disclosure relates generally to tint control, and moreparticularly, to a method and system for tint control for componentvideo signals.

2. Background of the Related Art

Common practice when decoding NTSC signals is for a “tint” or “hue”adjustment to compensate for possible differential phase errors betweena QAM chroma signal and its accompanying burst reference. Tintadjustment is also useful in compensating for other possible systemerrors.

Additionally, tint adjustment together with saturation adjustment allowsfor variations in personal preference to be accommodated, permitting anycolor to be shifted in saturation and hue without affecting the grayscale. In order to retain this capability for video signals that do notexperience NTSC decoding, such as component video signals, e.g., from aDVD player or set-top box, it is necessary to apply tint adjustment tothe baseband color difference signals.

The three main component video signals as known in the art are Y, B-Yand R-Y. Derived from the Y, B-Y and R-Y component video signals, Y/U/Vand Y/Pb/Pr are defined as follows: U=(B-Y)/2.03, V=(R-Y)/1.14,Pb=(B-Y)/1.772 and Pr=(R-Y)/1.402. U and V amplitude scaling is appliedin encoding an NTSC signal to prevent RF overmodulation as known in theart. Pb and Pr amplitude scaling is applied to parallel component videosignals to make each signal approximately equal to 0.7 Volt p-p.

Prior art tint control circuitry, as shown by FIG. 1, derive thebi-directional crosstalk components, i.e., +/−kU for coupling into V and−/+kV for coupling into U, necessary for tint control. The oppositepolarities associated with the bi-directional crosstalk components aresignificant, since they are equivalent to the effect of a tint controlin NTSC decoding which is derived as follows:

As known in the art, an NTSC chroma signal may be represented asfollows: C(t)=[V cos ωt+U sin ωt], 107 =2πfsc. Therefore, demodulating Vand U with 2 cos(ωt±φ) and 2 sin(ωt±φ), respectively, and tint rangebeing ±φ, the bi-directional crosstalk components can be derived.$\begin{matrix}{\begin{matrix}{V_{demodulation} = {\left\lbrack {{V\quad{\cos\left( {\omega\quad t} \right)}} + {U\quad{\sin\left( {\omega\quad t} \right)}}} \right\rbrack 2{\cos\left( {{\omega\quad t} \pm \phi} \right)}}} \\{= {{2V\quad{\cos({\omega\tau})}{\cos\left( {{\omega\quad t} \pm \phi} \right)}} + {2U\quad{\sin\left( {\omega\quad t} \right)}{\cos\left( {{\omega\quad t} \pm \phi} \right)}}}} \\{= {{V\left\lbrack {{\cos\left( {{2\omega\quad t} \pm \phi} \right)} + {\cos\left( {\pm \phi} \right)}} \right\rbrack} + {U\left\lbrack {{\sin\left( {{2\omega\quad t} \pm \phi} \right)} - {\sin\left( {\pm \phi} \right)}} \right\rbrack}}} \\{{= {{V\quad{\cos\left( {\pm \phi} \right)}} - {U\quad{\sin\left( {\pm \phi} \right)}}}},{{disregarding}\quad 2\omega\quad t\quad{terms}}} \\{{= {V - {U\quad{\sin\left( {\pm \phi} \right)}}}},{{for}\quad{small}\quad{values}\quad{of}\quad\phi}} \\{{= {V - {k\quad U}}},{k = {\sin\quad\phi}}}\end{matrix}\quad} \\{\begin{matrix}{U_{demodulation} = {\left\lbrack {{V\quad{\cos\left( {\omega\quad t} \right)}} + {U\quad{\sin\left( {\omega\quad t} \right)}}} \right\rbrack 2{\sin\left( {{\omega\quad t} \pm \phi} \right)}}} \\{= {{2V\quad{\cos({\omega\tau})}{\sin\left( {{\omega\quad t} \pm \phi} \right)}} + {2U\quad{\sin\left( {\omega\quad t} \right)}{\sin\left( {{\omega\quad t} \pm \phi} \right)}}}} \\{= {{V\left\lbrack {{\sin\left( {{2\omega\quad t} \pm \phi} \right)} + {\sin\left( {\pm \phi} \right)}} \right\rbrack} - {U\left\lbrack {{\cos\left( {{2\omega\quad t} \pm \phi} \right)} - {\cos\left( {\pm \phi} \right)}} \right\rbrack}}} \\{{= {{U\quad{\cos\left( {\pm \phi} \right)}} + {V\quad{\sin\left( {\pm \phi} \right)}}}},{{disregarding}\quad 2\omega\quad t\quad{terms}}} \\{{= {U + {V\quad{\sin\left( {\pm \phi} \right)}}}},{{for}\quad{small}\quad{values}\quad{of}\quad\phi}} \\{{= {U + {k\quad V}}},{k = {\sin\quad\phi}}}\end{matrix}\quad}\end{matrix}\quad$

As evident from FIG. 1, prior art tint control circuitry for highdefinition monitors and other imaging devices and appliances forobtaining the bi-directional crosstalk components +/−kU and +/−kV isgenerally complex. Further, the prior art tint control circuitry asshown by FIG. 1 employs two modulator/demodulator ICs, i.e., the MC1496balanced modulator/demodulator ICs which contains eight transistors, andperipheral circuitry, which add to the cost of the high definitionmonitors and other imaging devices and appliances.

A need therefore exists for a method and system for tint control forcomponent video signals which provide a non-complex approach forderiving the bi-directional crosstalk components necessary for tintcontrol.

SUMMARY OF THE INVENTION

The present disclosure provides a method and system for tint control forcomponent video signals. The system and method of the present disclosureprovide significant less complex circuitry and a less complex approach,respectively, for deriving the bi-directional crosstalk componentsnecessary for tint control. According to the present disclosure, thesystem of the present invention provides circuitry for receiving the Uand V component video signals and outputting U′ and V′ components, whichare equivalent to the bi-directional crosstalk components.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further explained by way of example and with referenceto the accompanying drawings, wherein:

FIG. 1 is a schematic diagram of prior art circuitry for deriving thebi-directional crosstalk components necessary for tint control; and

FIG. 2 is a schematic diagram of circuitry for deriving thebi-directional crosstalk components necessary for tint control accordingto the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 2 is a schematic diagram of a system having circuitry for derivingthe bi-directional crosstalk components U′ and V′ for tint controlaccording to the present invention. The system is designated generallyby reference numeral 100 and includes circuitry 110 for receiving videocomponent signals U and V, as well as a V control signal and operatingvoltages Vbb and Vcc. The circuitry 110 outputs tint control adjustmentsignals U′ and V′ to be used for tint control adjustment, where U′equals U−kV+2 ckV and V′ equals V+kU−2 ckU, and where k is a constant,and c is a value greater than or equal to zero and less than or equal toone, i.e., 0≦c≦1.

The circuitry 110 includes resistors R1-R16 and transistors Q1-Q8. Videocomponent signal V is received by input lead 120 connected to a firstterminal of resistors R1, R6 and R16. A second terminal of resistor R1and the collectors of transistors Q1 and Q2 are connected to output lead130. The output lead 130 provides the bi-directional crosstalk componentV′.

A first terminal of resistors R2 and R3 is connected to an emitter oftransistor Q1. The second terminal of resistor R3 is connected toground. The second terminal of resistor R2 is connected to a firstterminal of resistors R5 and R14. A base of transistor Q1 is connectedto a base of transistors Q2 and Q6 and a first terminal of resistors R9and R11. The base of transistor Q1 is also connected to operatingvoltage Vbb. The second terminal of transistor R14 is connected to abase of transistor Q4 and a first terminal of resistor R13. An emitterof transistor Q4 is connected to a first terminal of resistor R4. Asecond terminal of resistor R13 and a second terminal of resistor R13are connected to ground.

A collector of transistor Q3 is connected to operating voltage Vcc. Anemitter of transistor Q3 is connected to an emitter of transistor Q2 anda collector of transistor Q4. A base of transistor Q3 is connected to afirst terminal of resistor R12, a second terminal of resistor R11 and abase of transistor Q7. A second terminal of resistor R12 receives the Vcontrol signal via input lead 140.

An input lead 150 connected to the first terminal of resistor R5receives input signal U. A second terminal of resistor R5 outputs U′ viaoutput lead 160 and is connected to collectors of transistors Q5 and Q6.A second terminal of resistor R16 is connected to a base of transistorQ5 and a first terminal of resistor R15. An emitter of transistor Q5 isconnected to a first terminal of resistor R7. A second terminal ofresistors R7 and R15 is connected to ground. A second terminal ofresistor R9 is connected to a base of transistor Q8 and a first terminalof resistor R10. A second terminal of resistor R10 is connected toground.

A collector of transistor Q7 is connected to operating voltage Vcc. Anemitter of transistor Q7 is connected to an emitter of transistor Q6 anda collector of transistor Q8. An emitter of transistor Q8 is connectedto a second terminal of resistor R6 and a first terminal of resistor R8.A second terminal of resistor R8 is connected to ground.

To output the U′ and V′ signals, i.e., the tint control adjustmentsignals for the U and V component video signals, respectively, fixedprecision tint offsets are first applied by the circuitry 110 to eachcomponent color difference signal, i.e., the U and V component videosignals. Variable unidirectional “correction” of the opposite polarityis also applied, having a maximum correction of two times a fixedoffset, so that applying one-half the maximum variable offset,corresponding to mid-setting of the tint control, restores the tint to aneutral, unaltered condition.

During operation of the circuitry 110, the V component video signal istransformed into V′ by the total current supplied from Q1 and Q2. Q1supplies a fixed offset of +kU while Q2 supplies a variable offset of −2ckU, where 0<c<1 and is determined by the Q2/Q3 inter-base voltage, toprovide an output equal to V+kU−2 ckU which is equal to V′.

In similar fashion, U is transformed into U′ by the total currentsupplied from Q5 and Q6. Q5 supplies a fixed offset of −kV while Q6supplies a variable offset of +2 ckV, where 0<c<1 and is determined bythe Q6/Q7 inter-base voltage, to provide an output equal to U−kV+2 ckVwhich is equal to U′. One skilled in the art can appreciate that V istransformed into V′ and U is transformed into U′ by the circuitry 110,since the Q1 stage 162, which includes transistor Q1 and resistors R2and R3 is a non-inverting stage; the Q4 stage 164, which includestransistor Q4 and resistors R4 and R13 is an inverting stage; the Q5stage 166, which includes transistor Q5 and resistors R5, R7 and R16 isan inverting stage; and the Q8 stage 168, which includes transistor Q8and resistors R8, R9 and R10 is a non-inverting stage.

High accuracy and stability is ensured at tint center, due to the twobalanced differential amplifiers 170, 180. The first differentialamplifier 170 is mainly formed by transistors Q2, Q3 and Q4 and resistorR4, and the second differential amplifier 180 is mainly formed bytransistors Q6, Q7 and Q8 and resistor R8. The resistance of resistorsR4 and R8, as well as resistors R1-R3, R5-R7 and R9-R16 is selected toensure proper operation of the circuitry 110 in different applications,e.g., DC and AC applications.

Further, during operation of the circuitry 110, all of the transistorsQ1-Q8 are active at all times. During different times of operation, thecurrent is split between transistors Q2 and Q3 and transistors Q6 and Q7over a tint control range. Preferably, the system 100 is designed suchthat the current is split by having one-third of the current enteringthe differential amplifiers 170, 180 go to the left side of thedifferential amplifiers 170, 180 and two-thirds of the current enteringthe differential amplifiers 170, 180 go to the right side of thedifferential amplifiers 170, 180.

Unlike the prior art circuitry of FIG. 1, the system 100 of the presentinvention does impart varying DC level shifts into the U and V signalsas a function of the tint control setting. However, this is not aconcern in applications in which the signals are AC coupled and clampedin subsequent processing.

It will be understood that various modifications may be made to theembodiments disclosed herein and that the above description should notbe construed as limiting, but merely as exemplifications of preferredembodiments. Accordingly, those skilled in the art will envision othermodifications within the scope and spirit of the claims appended hereto.

1. A tint control system for component video signals comprising: a firstinput for receiving a first component video signal; a second input forreceiving a second component video signal; circuitry including a firstdifferential amplifier and a second differential amplifier for receivingthe first and second component video signals from the first and secondinputs, respectively, said first and second differencial amplifiers eachincluding a pair of transistors; a first output connected to thecircuitry for outputting a first tint control adjustment signal for thefirst component video signal; and a second output connected to thecircuitry for outputting a second tint control adjustment signal for thesecond component video signal, wherein a collector of one transistor ofeach pair of transistors of the first and second differential amplifiersis connected to an operating voltage.
 2. The system according to claim1, wherein the first outputted signal is represented as V+kU−2ckU, whereV represents the first component video signal, U represents the secondcomponent video signal, k is a constant, and c is a value greater thanor equal to zero and less than or equal to one.
 3. The system accordingto claim 1, wherein the second outputted signal is represented asU−kV+2ckV, where V represents the first component video signal, Urepresents the second component video signal, k is a constant, and c isa value greater than or equal to zero and less than or equal to one. 4.The system according to claim 1, wherein a base of a respectivetransistor of the pair of transistors of the first differentialamplifier is directly connected to a base of a respective transistor ofthe pair of transistors of the second differential amplifier.
 5. Thesystem according to claim 1, wherein the emitters of each pair oftransistors are connected to ground via a transistor connected in serieswith a resistor.
 6. A tint control system for component video signalscomprising: a first input for receiving a first component video signal;a second input for receiving a second component video signal; circuitryincluding a first differential amplifier and a second differentialamplifier for receiving the first and second component video signalsfrom the first and second inputs, respectively, said first and seconddifferential amplifiers each including a pair of transistors; a firstoutput connected to the circuitry for outputting a first tint controladjustment signal for the first component video signal; and a secondoutput connected to the circuitry for outputting a second tint controladjustment signal for the second component video signal, wherein acollector of one transistor of the pair of transistors of the firstdifferential amplifier is connected to the first input via a resistorand to the first output.
 7. A tint control system for component videosignals comprising: a first input for receiving a first component videosignal; a second input for receiving a second component video signal;circuitry including a first differential amplifier and a seconddifferential amplifier for receiving the first and second componentvideo signals from the first and second inputs, respectively, said firstand second differential amplifiers each including a pair of transistors;a first output connected to the circuitry for outputting a first tintcontrol adjustment signal for the first component video signal; and asecond output connected to the circuitry for outputting a second tintcontrol adjustment signal for the second component video signal, whereina collector of one transistor of the pair of transistors of the seconddifferential amplifier is connected to the second input via a resistorand to the second output.
 8. A tint control system for component videosignals comprising: a first input for receiving a first component videosignal; a second input for receiving a second component video signal;circuitry including a first differential amplifier and a seconddifferential amplifier for receiving the first and second componentvideo signals from the first and second inputs, respectively, said firstand second differential amplifiers each including a pair of transistors;a first output connected to the circuitry for outputting a first tintcontrol adjustment signal for the first component video signal; and asecond output connected to the circuitry for outputting a second tintcontrol adjustment signal for the second component video signal, whereina base of one transistor of the pair of transistors of the firstdifferential amplifier is connected to a third input via a resistor forreceiving a control signal for the first component video signal.
 9. Atint control system for component video signals comprising: a firstinput for receiving a first component video signal; a second input forreceiving a second component video signal; circuitry including a firstdifferential amplifier and a second differential amplifier for receivingthe first and second component video signals from the first and secondinputs, respectively, said first and second differential amplifiers eachincluding a pair of transistors; a first output connected to thecircuitry for outputting a first tint control adjustment signal for thefirst component video signal; and a second output connected to thecircuitry for outputting a second tint control adjustment signal for thesecond component video signal, wherein a base of one transistor of thepair of transistors of the second differential amplifier is connected toa third input via a resistor for receiving a control signal for thefirst component video signal.
 10. A method for controlling tint ofcomponent video signals, the method comprising the steps of: receiving afirst component video signal; receiving a second component video signal;providing circuitry including a first differential amplifier and asecond differential amplifier for receiving the first and secondcomponent video signals, respectively, the first and second differentialamplifiers each including a pair of transistors; outputting a first tintcontrol adjustment signal for the first component video signal; andoutputting a second tint control adjustment signal for the secondcomponent video signal, wherein a collector of one transistor of eachpair of transistors is connected to an operating voltage.
 11. The methodaccording to claim 10, wherein the first outputted signal is representedas V+kU−2ckU, where V represents the first component video signal, Urepresents the second component video signal, k is a constant, and c isa value greater than or equal to zero and less than or equal to one. 12.The method according to claim 10, wherein the second outputted signal isrepresented as U−kV+2ckV, where V represents the first component videosignal, U represents the second component video signal, k is a constant,and c is a value greater than or equal to zero and less than or equal toone.
 13. The method according to claim 10, wherein a base of arespective transistor of the pair of transistors of the firstdifferential amplifier is directly connected to a base of a respectivetransistor of the pair of transistors of the second differentialamplifier.
 14. The method according to claim 10, wherein the emitters ofeach pair of transistors are connected to ground via a transistorconnected in series with a resistor.
 15. A method for controlling tintof component video signals, the method comprising the steps of:receiving a first component video signal; receiving a second componentvideo signal; providing circuitry including a first differentialamplifier and a second differential amplifier for receiving the firstand second component video signals, respectively, the first and seconddifferential amplifiers each including a pair of transistors; outputtinga first tint control adjustment signal for the first component videosignal; and outputting a second tint control adjustment signal for thesecond component video signal, wherein a collector of one transistor ofthe pair of transistors of the first differential amplifier is connectedto an input via a resistor for receiving the first component videosignal and to an output for outputting the first signal.
 16. A methodfor controlling tint of component video signals, the method comprisingthe steps of: receiving a first component video signal; receiving asecond component video signal; providing circuitry including a firstdifferential amplifier and a second differential amplifier for receivingthe first and second component video signals, respectively, the firstand second differential amplifiers each including a pair of transistors;outputting a first tint control adjustment signal for the firstcomponent video signal; and outputting a second tint control adjustmentsignal for the second component video signal, wherein a collector of onetransistor of the pair of transistors of the second differentialamplifier is connected to an input via a resistor for receiving thesecond component video signal and to an output for outputting the secondsignal.
 17. A method for controlling tint of component video signals,the method comprising the steps of: receiving a first component videosignal; receiving a second component video signal; providing circuitryincluding a first differential amplifier and a second differentialamplifier for receiving the first and second component video signals,respectively, the first and second differential amplifiers eachincluding a pair of transistors; outputting a first tint controladjustment signal for the first component video signal; and outputting asecond tint control adjustment signal for the second component videosignal, wherein a base of one transistor of the pair of transistors ofthe first differential amplifier is connected to an input via a resistorfor receiving a control signal for the first component video signal. 18.A method for controlling tint of component video signals, the methodcomprising the steps of: receiving a first component video signal;receiving a second component video signal; providing circuitry includinga first differential amplifier and a second differential amplifier forreceiving the first and second component video signals, respectively,the first and second differential amplifiers each including a pair oftransistors; outputting a first tint control adjustment signal for thefirst component video signal; and outputting a second tint controladjustment signal for the second component video signal, wherein a baseof one transistor of the pair of transistors of the second differentialamplifier is connected to an input via a resistor for receiving acontrol signal for the first component video signal.